1. Field of the Invention
The present invention generally pertains to UV-curable ink formulations that are capable of being cured under low-energy conditions and methods for creating a printed ink image on a substrate using the ink. In particular, the ink formulations may be cured using conventional high-wattage bulbs operated at half or less of the bulb's nominal wattage.
2. Description of the Prior Art
Traditional UV-curable ink printing systems commonly utilize high-wattage bulbs (e.g., greater than 200 W) to deliver the necessary UV light energy to initiate the free-radical polymerization processes that result in curing of the ink onto the substrate to which it has been applied. The use of bulbs that emit these high energy levels has heretofore been critical to the prevention of oxygen inhibition during the cure process and to facilitate rapid cure times so that press throughput can be optimized. However, the use of high-wattage bulbs presents a number of concerns. As can be readily appreciated, the energy usage to operate equipment with high-wattage bulbs is quite high. Apart from the energy usage associated with the direct operation of the bulbs themselves, there are also indirect energy consequences as well. These bulbs also tend to emit relatively large amounts of heat energy when operated, which may need to be countered with more powerful climate control systems. In addition, the heat energy produced limits the ability of the printer to utilize heat-sensitive substrates, such as certain types of plastics and films that can warp under even fairly mild elevated temperature conditions.
With electrical power grids being taxed to their practical limits, municipalities and utilities often are forced to impose energy caps on businesses. In the case of a printer utilizing a large number of printing presses with high-wattage bulbs, these caps either mean that the printer may encounter limits in production and an inability to grow its business through the addition of more printing presses. Consequently, a need exists in the art for an ink system that is capable of curing under exposure to lower-energy conditions without sacrificing line speed.